Fin construction



March 22, 1960 K. A. wEATHERwAx ETAL 2329308 FIN coNsTRucTIoN Filed April 27, 1955 5 'z 9 7 INVENToRs KEN/VET/-l A. WEATHERWAX LEM/AS` R SMITH, 'JOHN E PERSO/V United FIN CONSTRUCTIN Kenneth A. Weatherwax, Lewis R. Smith, and John. F. Pearson, Jackson, Mich., assignors to Acme Industries, Inc., Jackson, Mich., a corporation of Delaware Application April 27, 1955, Serial No. 504,228

1 Claim. (Cl. 138-38) .The present invention relates to heat exchange tubes, and more particularly to tubes of this class having internal fins arranged to promote vbetter heat transfer between a fluid outside the tube and a fluid fiowing within the tube.

Heretofore, the art has sought to provide internally fin heat exchange tubes in which the fluid flowing within the tube would give up heat to or receive heat from the extended surface areas of the fins past which it flowed, which fins would intnrn give up heat to or receive heat from the outside wall of the tube. In this way, the heat transfer between fiuids outside and inside vthe tube has been somewhat increased. ln an eifort to provide internally finned tubes adapted to enjoy this increased heat transfer, it has been proposed to form the tubes with integral fins extending inwardly from the side walls thereof and formed by machining or extruding or the like. However, it has not been possible to increase the interior surface of the tube by substantially more than one hundred percent by this arrangement; and the cost of manufacturing such tubes has been quite high. Moreover, it has been both difficult and expensive to remove the portions of the fins adjacent the tube ends when it has been desired to install the tubes as in the tube Sheet of a heat exchange device.

In a further eifort to provide suitable internally fin tubes of this type, it has been proposed to insert the fins within the tubes separately and then fasten them to the tube walls as by soldering or brazing or riveting or the like. However, it has been found in practice that such lin assemblies readily break loose from their attachments and are extremely difficult to assemble. Moreover, the inserts which have heretofore been used have been found to give a much smaller increase in heat transfer than in the case of integral internal fins, and in some cases have been found to increase the heat transfer hardly at all.

Although many attempts Were made to overcome the foregoing difliculties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial Scale.

It has now been dscovered that if the fin assemblies are actually embedded in the interior wall of the tube, the heat exchange tube assemblies may be quickly and inexpensively assembled and will prove strong and durable, but most important, will give greatly increased heat exchange performance.

Accordingly, it is an object of the present invention to provide heat exchange tubes having improved heat exchange characteristics.

Another object of the invention is to provide heat exchange tubes having fin inserts which may readily be formed by extrusion or the like.

The invention also contemplates providing heat exchange tubes having internal fin assemblies which may be quickly and easily applied to the interior of the tube.

It is a further object of the invention to provide methods of manufacturing heat exchange tubes having the foregoing characteristics.

'bodiment of heat exchange tube according to our invention, taken on the line 2-2 of Figure 1;

Figure 3 shows a partially assembled modification of heat exchange tube according to our invention as viewed in Figure 2;

Figure 4 llustrates the embodiment of Figure 3 completely assembled;

Figure 5`is a cross-sectional view of still another modification of our invention at an initial stage of assembly;

Figure 6 is another view of the embodiment of Figure 5 shown after assembly is completed; and

Figure 7 is a greatly enlarged fragmentary cross-sectional view of a portion of a heat exchange according to our invention, as seen on the line 7-7 of Figure 1.

Referring now to the drawing in greater detail, v'we have shown in Figures 1 and 2 a heat exchange tube indicated generally at 1 and comprising an outer hollow metal tubular member 3 having therein a fin member 5 comprsing a plurality of radially extending longitudinally disposed fins 7 having at their outer ends circumferentially spaced longitudinally extending edges 9. The tubular member arid fin member of Figures 1 and 2, as in the case of the corresponding members in the embodiments to follow, are preferably made of soft metals having high coefficience of thermal conductivity such as copper or aluminum or the like. In practice it has been found desirable that the tubular member 3 be formed of copper and that the fin member 5 be formed of such an aluminum alloy, as for example, 63S-T5, 63S-T6 or 63S-T2, properly aged. Materials such Vas these aluminum alloys may be readily extruded to the desired shape."

The' tube of Figures l and 2 may be assembled by inserting fin member 5 within tubular member 3 and then reducing tubular member 3 as by die rolling or s'waging or the like so as to form an interference fit between edges 9 and the interior wall surface of member 3. In Figure 7, we have shown somewhat diagrammatically a greatly enlarged fragment of Figures 1 and 2 taken on the line 7- 7 of Figure 1, which shows how a iin 7 will actually penetrate the member 3 when the two are brought into interference fit and will become embedded in member 3. Fns 7 actually become embedded in member 3, as shown in Figure 7; and the adjacent metal of member 3 actually tends to build up on either side of edges 9 when fin 7 is embedded in member 3, much in the way of a meniscus, as shown in Figure 7. This embedding of the fins in the tube walls forms a very important part of our invention, since it has been found that the heating transfer between fins 7 and member 3 is very greatly increased by this construction, as compared to a construction in which the fin members are held against the outer tubular wall by welding or riveting or brazing or the like. Although the scientific principle involved is not known With certainty, it is believed that in the course of embedding the fins in the outer wall, a very intimate, even atomic, contact is made between the respective metals, which intimate contact permits heat fiow in substantially the same manner as in the case of a fin assembly which has been formed integrally with straightened within tubular member 3 as by having their radii of curvature increased, edges 9 lwill move substan-` portion 15.` Figure 3 shows the first stage of assembly` of the tube according to this embodiment; and as therein shown, fin members 11 are inserted one by one soas to to form by extrusion or otherwise. The tubular member may then be reduced as by die rolling or swaging or the like; or edges 13 may be embedded in the tubular member by forcing them radially outwardly by increasing the radius of curvaturefof web portions 15.l To this latter end, a mandrel may be passed through the internal void defined by the three fin members 11, in interference contact with the crown of each web portion 15 so as to reduce the radii of curvature of these Web portions and press edges 13 into the tubular member. In Figures and 6, we have shown still another embodiment of heat exchange tube according to our invention,V in which assemblyis effected by inserting a pair of complementary fin members 17 within the tubular member, each fin member terminating in a pair of circuinferentiaily spaced longitudinal edges 19 and having along opposite sides thereof a pair of concavely curved portions 21 spaced apart by a relatively fiat medial web portion 23. The radii of curvature of portions 21 may then be reduced by passing a mandrel through the interior voids as in the case of the embodiment of Figures 3 and 4 whereupon these portions will become straightened Vor partially straightened. Medial web portions 23 Will thus be brought into abutment and will press against each other, which pressure will be transmitted back to edges 19 to embed them somewhat within the tubular member. Accordingly, it willbe seen that we have provided'heat exchange tubes which have extremely efi'icient heat trans fer characteristics and yet are simple and inexpensive in construction and rugged and durable inv use. Moreover, it will be seen that we have provided methods for manufacturing heat exchange tubes which may be practiced cheaply with a minimum of equipment to produce with form a hollow fin assembly which would be very ldiflicult characteristics.

Thus, it will be seen that We have achieved all of the objects of our invention.

Although the presentrinvention has been described in conjunction With preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the 'spirit and scope of the invention; as those skilled in the art will readily understand. Such modifications and variations are considered 'to be within the purview and scope of the invention and appended claim.

We claim: l

A heat exchange Vtube for conducting a refrigerant comprising an outer tubular member of relativeiy soft contractible copper and an internal fin member disposed in said tubular member, said fin member being an aluminum alloy harder and more resilient than the copper material of said tubular member, said fin member being of an integral construction and having a plurality of radial fins of similar'V form and spacing extending outwardly from a common central core into intimate, unbonded, heat-conductive contact with the inner surface of said tubular member at the outer circumferential ends of said fins, said radial fins each having a cross section increasing in tbickness from a point adjacent said core outwardly toward said inner surface, said outer circumferential ends of said fins having an interference fit with said inner surface, said fins being disposed out of diametrical relation with each other so as to augment the deection of said fins upon radial leading, said enter circumferentiai ends of'said fins each having that stres-sed abutment relation with said inner surface which results from a radial contraction of said tubular member upon said fin member to provide said interference fit within the elastic limit of said fins.

References Cited in the file of this patent UNITED STAT ES PATENTS 

